Patellar joint prostheses are not new. They have been used in the past to repair damaged or diseased knee joints, often in conjunction with other prosthetic components for a total or partial knee replacement.
A patellar joint prosthesis is normally implanted on the back of the patella to replace the natural surface which articulates with the femoral component. The surgical process includes everting the patella and removing the diseased or damaged articulating surface. The patellar joint prosthesis is then attached to the bone, and the joint is reassembled.
In the past patellar joint prostheses have comprised a relatively flat bone facing surface and a contoured surface opposite the bone facing surface. When the joint is reassembled, the contoured surface articulates with the femoral component of the knee joint, whether they are natural or prosthetic.
In the past the bone facing surface of the prosthesis included a protuberance for attaching that surface to the everted patella. The protuberances have varied in shape. The most common such protuberances are a plurality of pins, normally three or four, which are pressed into the patella. Solid shapes such as crosses have also been used.
The protuberances used in the past have been effective. However, there is always a desire to find improved means for attaching the prosthetic patellar joints to the patella. An improved means for attachment would be one which shows increased resistance to shear displacement between the prosthesis and the patella.